Increasing use of loads supplied by electronic power converters in industry has led to growing problems with the reliability of the power supply. Computers, adjustable speed drives, and automated manufacturing processes are very sensitive to voltage sags and brief outages. The need for greater power quality has prompted the use of uninterruptable power systems and/or other electronic power conditioning means to maintain the voltages within the susceptibility levels of the critical equipment. Nonetheless, the prior art has not been able to raise the power quality levels to meet these requirements. However, a new family of power converters developed by the present inventor and described in the aforementioned copending application permits improvement of power quality levels to meet the greater challenges posed by the above noted problems.
Historically, thyristor controlled equipment, such as the High Voltage Direct Current (HVDC) transmission systems and Static VAR Compensators (SVC), have been used extensively in power system applications. However, the use of gate turn-off devices in power systems has not been viable until recent progress in semiconductor devices. The use of the Static Condenser (STATCON) and the Unified Power Flow Controller (UFC) to realize power flow control in transmission systems was proposed as high performance alternatives to conventional thyristor based Static VAR Compensators by Gyugyi, in "A Unified Power Flow Control Concept for Flexible AC Transmission Systems", IEE 5th International Conference on AC and DC Transmission, 1991, London. Development activities related to these devices have thyristor based Static VAR Compensators. However, development activities related to these devices have primarily focused towards control of power flow at the transmission level under the Flexible AC Transmission Systems (FACTS) program.
The use of gate turn-off device technology to realize control at the distribution level was proposed under the framework of the Custom Power program initiated by the electric Power Research Institute (EPRI), in "Recent Development: EPRI's Custom Power Concept", H. Mehta, Proceedings of Power Quality '93 Conference, Intertec International Inc., Ventura, Calif., pp. 794-795, October, 1993.
The concept of Custom Power introduces a supply-side alternative to consumer installed uninterruptable and standby power systems. Custom Power meets the critical power needs of the customer and provides large energy users with reliable electric power with built-in redundancies and fault tolerances and higher efficiency. This approach is expected to yield major energy savings resulting from the elimination of energy storage and retrieval stages. STATCONs and solid state breakers have been proposed to provide a more reliable supply in such cases.